The study compared patients with the same severity of symptoms in four hospitals in Germany which had locked doors, and 16 which did not.

There was no difference in the rates of patients leaving without permission or hurting themselves, it found.

Oxford University psychiatry professor Tom Burns, whose commentary on the study was also published in The Lancet, told Nine To Noon an open-door policy could be preferable for those with depression, anxiety or psychosis, as it promoted a better therapeutic atmosphere and more positive health outcomes.